Does each need an equal amount of s?

Let's say I have

<tr>
   <td>Hi</td>
   <td>Hi</td>
   <td>Hi</td>
   <td>Hi</td>
   <td>Hi</td>
</tr>
<tr>
   <td>Bye</td>
   <td>Bye</td>
</tr>

without any colspan attributes. Both Chrome and Firefox will correctly render the two cells of the second row and then leave "3 TRs of empty space".

My question is: Is this actually syntactically allowed in HTML or something the browsers are merely "auto-fixing"?